[SystemZ] Mark CC defs as dead whenever possible.

Marking implicit CC defs as dead everywhere except when CC is actually
defined and used explicitly, is important since the post-ra scheduler
will otherwise insert edges between instructions unnecessarily.

Also temporarily disable LA(Y)-> AGSI optimization in
foldMemoryOperandImpl(), since this inroduces a def of the CC reg,
which is illegal unless it is known to be dead.

Reviewed by Ulrich Weigand.

llvm-svn: 268215

llvm/lib/Target/SystemZ/SystemZElimCompare.cpp

@@ -216,7 +216,7 @@ SystemZElimCompare::convertToBRCT(MachineInstr *MI, MachineInstr *Compare,
     .addOperand(MI->getOperand(0))
     .addOperand(MI->getOperand(1))
     .addOperand(Target)
-    .addReg(SystemZ::CC, RegState::ImplicitDefine);
+    .addReg(SystemZ::CC, RegState::ImplicitDefine | RegState::Dead);
   MI->eraseFromParent();
   return true;
 }
@@ -448,7 +448,7 @@ fuseCompareAndBranch(MachineInstr *Compare,
     // to a non-fused branch because of a long displacement.  Conditional
     // returns don't have that problem.
     MIB.addOperand(Target)
-       .addReg(SystemZ::CC, RegState::ImplicitDefine);
+       .addReg(SystemZ::CC, RegState::ImplicitDefine | RegState::Dead);
   }
 
   if (Type == SystemZII::CompareAndSibcall)

llvm/lib/Target/SystemZ/SystemZInstrInfo.cpp

@@ -737,6 +737,14 @@ static LogicOp interpretAndImmediate(unsigned Opcode) {
   }
 }
 
+static void transferDeadCC(MachineInstr *OldMI, MachineInstr *NewMI) {
+  if (OldMI->registerDefIsDead(SystemZ::CC)) {
+    MachineOperand *CCDef = NewMI->findRegisterDefOperand(SystemZ::CC);
+    if (CCDef != nullptr)
+      CCDef->setIsDead(true);
+  }
+}
+
 // Used to return from convertToThreeAddress after replacing two-address
 // instruction OldMI with three-address instruction NewMI.
 static MachineInstr *finishConvertToThreeAddress(MachineInstr *OldMI,
@@ -750,6 +758,7 @@ static MachineInstr *finishConvertToThreeAddress(MachineInstr *OldMI,
         LV->replaceKillInstruction(Op.getReg(), OldMI, NewMI);
     }
   }
+  transferDeadCC(OldMI, NewMI);
   return NewMI;
 }
 
@@ -842,19 +851,26 @@ MachineInstr *SystemZInstrInfo::foldMemoryOperandImpl(
   unsigned Size = MFI->getObjectSize(FrameIndex);
   unsigned Opcode = MI->getOpcode();
 
+// XXX This is an introduction of a CC def and is illegal! Reactivate
+// with a check of liveness of CC reg.
+#if 0
   if (Ops.size() == 2 && Ops[0] == 0 && Ops[1] == 1) {
     if ((Opcode == SystemZ::LA || Opcode == SystemZ::LAY) &&
         isInt<8>(MI->getOperand(2).getImm()) &&
         !MI->getOperand(3).getReg()) {
       // LA(Y) %reg, CONST(%reg) -> AGSI %mem, CONST
-      return BuildMI(*InsertPt->getParent(), InsertPt, MI->getDebugLoc(),
+      MachineInstr *BuiltMI =
+        BuildMI(*InsertPt->getParent(), InsertPt, MI->getDebugLoc(),
                      get(SystemZ::AGSI))
           .addFrameIndex(FrameIndex)
           .addImm(0)
           .addImm(MI->getOperand(2).getImm());
+      BuiltMI->findRegisterDefOperand(SystemZ::CC)->setIsDead(true);
+      return BuiltMI;
     }
     return nullptr;
   }
+#endif
 
   // All other cases require a single operand.
   if (Ops.size() != 1)
@@ -870,11 +886,14 @@ MachineInstr *SystemZInstrInfo::foldMemoryOperandImpl(
       isInt<8>(MI->getOperand(2).getImm())) {
     // A(G)HI %reg, CONST -> A(G)SI %mem, CONST
     Opcode = (Opcode == SystemZ::AHI ? SystemZ::ASI : SystemZ::AGSI);
-    return BuildMI(*InsertPt->getParent(), InsertPt, MI->getDebugLoc(),
+    MachineInstr *BuiltMI =
+      BuildMI(*InsertPt->getParent(), InsertPt, MI->getDebugLoc(),
                    get(Opcode))
         .addFrameIndex(FrameIndex)
         .addImm(0)
         .addImm(MI->getOperand(2).getImm());
+    transferDeadCC(MI, BuiltMI);
+    return BuiltMI;
   }
 
   if (Opcode == SystemZ::LGDR || Opcode == SystemZ::LDGR) {
@@ -963,6 +982,7 @@ MachineInstr *SystemZInstrInfo::foldMemoryOperandImpl(
       MIB.addFrameIndex(FrameIndex).addImm(Offset);
       if (MemDesc.TSFlags & SystemZII::HasIndex)
         MIB.addReg(0);
+      transferDeadCC(MI, MIB);
       return MIB;
     }
   }

llvm/lib/Target/SystemZ/SystemZShortenInst.cpp

@@ -143,7 +143,7 @@ bool SystemZShortenInst::shortenOn001AddCC(MachineInstr &MI,
 					   unsigned Opcode) {
   if (!LiveRegs.contains(SystemZ::CC) && shortenOn001(MI, Opcode)) {
     MachineInstrBuilder(*MI.getParent()->getParent(), &MI)
-      .addReg(SystemZ::CC, RegState::ImplicitDefine);
+      .addReg(SystemZ::CC, RegState::ImplicitDefine | RegState::Dead);
     return true;
   }
   return false;